Restoring teeth that are endodontically treatedthrough existing crowns. Part i: Survey of pulpalstatus on access

Glenn Trautmann, DMDVJames L. Gutmann, DDSVMartha E, Nunn, DDS, PhDVDavid E. Witherspoon, BDSc, MS''/Jay D. Shulman, DMD, MA,

Endodontics

Objective: The purpose ot this study was to identify the pulpal findings encountered by practitioners whenaccessing eompiete-coverage crowns that require nonsurgical rool canal treatment and the reievance otcoronai leakage to the success of the RTC. Method and materials: The survey package consisted of acover letter stating the instructions, rationaie, and purpose for the questionnaire, a questionnaire with 8short-answer questions, and a stamped, se II-ad dressed envelope. A randomized sampie ot active dentists(300 general practitioners. 300 prosthodontists, and 300 endcdontists) was selected. Coiiected data wereanalyzed with the chi-square test. Results: A 60% response rate was obtained. Statistically significant dil-lerences were found among the practitioner groups, depending on the question. Genera! practitioners andendodontists obtain access through crowns and maintain tfiese crowns as tinal restoration significantiymore often than do prosthodontists Practitioners responded that teeth witfi compiete crowns require non-surgicai root canai treatment atter 5 to 10 years. Conclusion: Respondents believe that leakage must beaddressed when endodontic access cavities in artificial crowns are restored after nonsurgical root canaitreatrtient. General practitioners perform nonsurgicai root canai treatment more frequently than doprosthodontists. Practitioners indicated that when teeth with complete crowns require nonsurgical rootcanal treatment, treatment is most often performed 5 to 10 years after placement of the crown,(Quintessence tnt 2000:31:713-718)

Key words: compiete-coverage crown, endodontist, gênerai practitioner, leakage, prosthodontist, rootcanai treatment, survey

CLINICAL RELEVANCE: This report wili help to estab-lish guidelines for an evidence-based study to identifywhich materials minimize leakage when crowned teeththat require nonsurgical root canal treatment arerestored.

'Graduate Resident-Graduate Endodontics. Department ot RestorativeSciences, Baylor Coiiege ol Dentistry, Te^as ASM University System,

Healtti Science Center, Oailas. Texas.

^Professor and Director of Graduate Endodontics, Department oíRestorative Sciences. Baylor Coitege of Dentistry, Texas ASM University

System, Healtii Science Centei, Dallas, Teias.

^Assistant Professor. Department of Public Health Sciences, Baylor

College ol Dentistry, Texas ASM university System, Health Science

Center, Dallas, Texas.

'Assistant Prolessor-Graduate Endodontics, Department ot RestorativeSciences, Baylor College of Dentistry, Texas ASM University System,

Health Science Centei. Dallas, Teias

^Associate Professor, Department oí Public Healtti Sciences. BaylorCollege of Dentistry, Texas ASM University System, Health ScienceCenter. Dallas, Texas.

Reprint requests: Dr James L Gutmann, Baylor Coiiege of Dentistry,Graduate Endodontics (Roorr 335). 3302 Gaston Avenue. Dailas, Texas75246.E-maihjgutmann@tamDcd.edu

Complete-coverage artificial crowns provide thebest treatment option for teeth that have large

detective restorations. The crown protects the toothfrom further insult and maintains it as a functional,esthetic unit. Some teeth may also receive this treat-ment to maintain or enhance the health of the peri-odontum. In spite of these advantages, between 2%and 24''.'o of teeth restored with complete coronalrestorations show subsequent signs of pulpal disease ordegeneration that requires nonsurgical root canal ther-apy,'"̂ Endodontists estimate that 20% to 50«/o of theircases involve teeth with complete-coverage crowns.̂

The cumulative insult of periodontal disease andtreatment/-'" caries,"-''' and restorative procedures'^-"often impacts the integrity of the dental puip.Mechanical cutting of tooth structure with high-speedrotary instruments, the toxic effects of some materialsapplied to freshly cut dentin, and the adherence ofbacterial piaque to dentin surfaces are major factorsthat result in irreversible inflammatory changes in thepulp.''""'^' The additive effect of these results in atooth with a complete-coverage restoration and seri-ously compromised pulpal health. Signs and symp-

ÛLiintessence International713

• TrautrTiann et al

toms may or may not be present during this process,even if the pulp has undergone necrosis,^-

Nonsurgicai root canal treatment (NSRCT) must beregarded as incomplete until a proper coronal restora-tion is placed. This restoration is an integral part ofestablishing a barrier between the periradicular tissueand the ora! cavity,̂ '̂̂ '* Poor selection of restorativematerial or lack of a restoration may adversely affectthe seal of the root filling, resulting in bacterial conta-mination of an otherwise favorable root canal treat-ment,-' The technical quality of a coronal restorationis as significant as and, in some cases, may be moreimportant than, the technical quality of the endodon-tic treatment in achieving and maintaining apical peri-odontal health,-'* This finding emphasizes that leakageis an ongoing process pertinent to all aspects of treat-ment. The materials available today, however, areunable to totally prevent this process of leakage, cithersingularly or in combination.

Surveys have been described as important informa-tion tools that can identify present conditions and detailcurrent philosophies, techniques, and needs,̂ '̂ ^ Oncethe informafion is gathered, it can provide an overviewof treatment rafionales, which, when combined with sci-entific data and empirical, clinically reliable techniques,may lead to higher rates of successful outcomes in prac-tice. Furthermore, key informafion may be gathered andtabulated in a timely fashion, assuring evidence-basedguidelines for a scientific study,̂ ^

The purpose of this study was to identify the pulpalfindings encountered by practitioners when theyaccess complete-coverage crowns that require NSRCTand the relevance of restoring this access permanently,in terms of coronal leakage. This information will helpto establish guidelines for an evidence-based study toidentify whieh materials minimize leakage in therestoration of crowned teeth that require NSRCT,

METHOD AND MATERIALS

The design of the questionnaire for this study wasdeveloped by a focus group of faculty from the disci-plines of biostatistics and endodontics. The surveyitems were created to address a number of unresolvedclinical issues. These issues included the pracfifioner'sunderstanding of coronal leakage and the practi-tioner's preference of contemporary restorative mate-rials to be used with various types of complete-cover-age crowns. The questions focused on the clinicalscenario of endodontically accessed teeth with preex-isting complete-coverage crowns.

The survey package consisted of a cover letter statinginstructions, rationale, and purpose for the question-naire, the questionnaire itself, and a stamped, self-

addressed envelope. The survey had 8 short-answerquestions. The questions applicable to this portion of thestudy are shown in Fig 1, The faculty focus group, aswell as a group of endodonfic graduate students, pre-tested the survey to ensure that the questions were clear,succinct, and accurately addressed the issues of interest,

A power anaiysis was used to identify the number ofsurveys required for a valid statistical analysis with aminimum of bias, assuming an anticipated response rateof 50°.'(i, The random sample consisted of 900 dental pro-fessionals, including active general practitioners (300),active prosthodontists (300), and active endodonfists(300) throughout the United States. Mailing labels forthese randomized groups were obtained from the follow-ing 3 associations, respectively: the American DentalAssociation, the American Association of Prostho-dontists, and the American Associafion of Endodontists,

The survey covered different aspects of clinical sce-narios and the dentists' choice of restorative materialfor sealing access openings following nonsurgicalendodontic treatment through the various types ofcomplete-coverage crowns. In part 1 of this survey,different case situations encountered in practice wereaddressed, including the longevity and failure ofcrowns, and pulpal condition, and the practitioners'views on the relevance of leakage to the ultimate suc-cess of the crown. Part 2 of this survey addressed therespondents' attitudes toward permanent restorationof teeth recently subjected to NSRCT and specificrestorative techniques for sealing the access cavity ofteeth treated through complete-coverage crowns,̂ °

After an interval of 60 days, a low response rate(16%) from general practitioners triggered a secondmailing of the same questionnaire. After 90 days, alldata were collected and analyzed statistically.Frequency tables and descriptive statistics were com-piled for the various survey items. The atfitudes andpractices of general practitioners, prosthodontists, andendodontists, as ascertained from this survey, werecompared using chi-squared tests of independence. Allstatistical analyses were performed with SPSS statisti-cal software (version 9,0, SPSS),

RESULTS

Nine hundred surveys were mailed initially within atime span of 90 days. Of the 900 surveys sent out, 543were completed and returned, representing a 60°hresponse. This section of the survey targeted the issue ofthe longevity and failure of crovms, the pulpal condidonon entry through a complete-coverage crown, therespondents' attitudes toward restoration of teethrecently subjected to NSCRT, and their views on therelevance of lealiage to the success or failure of NSRCT.

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• Trautmann et ai

Fig 1 Questionnaire iiems. (RCT) Root canal treatment.

I practice as a (an):

i j Endodcntist,J Prosthodontist.LJ General practitioner.

Wnen doing root canal treatment (RCT) through a crownedtooth, the most frequent puip status I encounter is

3 Necrosis %.J Irreversibie pulpitis %.J I do not do RCT %.3 Other %.

Wtien pertorming RCT on a tooth with an arfificiai crown, I:

J Go through the crown and restore access openingafter RCT %.

J Remove the crown, use as a temporary crown, andthen recement the originai crown after RCT %.

"J Remove the crown, use as a temporary, and makea new crown after RCT ,%.

Ü Remove the crown, make a temporary crown, and thencreate a new crown after compietion of the root oanaitherapy %.

3 Other

I consider coronai ieakage as an important factor whenrestoring an access opening through a crown'

J Always.^ Frequently.3 Seldom,Zi Never.

In your practice, when RCT is needed on a crowned tooth,what is ttie approximate age of the crown?

Ü 0 to 1 year.Q 1 to 5 years.Ü 5to 10 years.Q 10 to 15 years.^ 15 years or more.

The overall response rate to the first question {prac-tice type) was eoa/o (543/900). Table 1 details tbenumber of responses from each practitioner group. Allpractitioner groups had similarly high response rates;at least 55% of each practitioner group responded tothis question.

The overall response rate to the second question(pulpal status) was 71% (346/543) (Table 2). Therewas a statistically significant difference (P < 0.001)between tbe response rate of prostbodonttsts(14/72=41%) and tbose of the other 2 groups of prac-titioners (endodontists, 191/191=100%; general prac-

titioners, 86/120=72%) who access teeth and identitythe pulpal status. Most prosthodontists (58/72 [81%])indicated, in the response "other," that they do notperform root canal treatment and added that theyrefer patients to an endodontist. Only 28% (34/120)of general practitioners refer patients to endodontists.

Further data collected from the second question(puipai statis) indicated that endodontists and prostho-dontists indentified the findings of necrosis and irre-versible pulpitis on an equivalent basis (50% necrosis& 50% irreversible pulpitis) in symptomatic teeth withcomplete-coverage crowns. General practitioners iden-tified necrosis in 70% of tbe eases and irreversible pul-pitis in 30% of cases. Because of tbe small number ofresponses from prosthodontists (47%), there was statis-tically more of a difference in tbe response betweenendodontists and prostbodontists than there wasbetween endodontists and general pratitioners.

The overall response rate to the tbird question(access route) was 70% (382/543). The responses tothe question were categorized into 3 groups: (1) thosewho go through the crown to access the pulp cham-ber; (2) tbose wbo obtain access for NSRCT byremoving tbe crown and using this crown as perma-nent restoration; and (5) those who obtain access forNSRCT with the original crown remaining as tempo-rary, or making a provisional crown and creating anew complete coverage crown (Table 3). A statisticallysignificant difference in tbe number of responses wasrecorded {P < 0.001) between prostbodontists (37%)and tbe otber 2 groups of practitioners (endodontists,100%; general practitioners, 69%).

Tbe following data was obtained by those practi-tioners who responded "otber" in tbe third question,in which no access route was selected by the practi-tioners: Sixty-tbree percent (110/175) of the prostho-dontists refer the patients to an endodontist for thetotal procedure while only 30% (51/166) of generalpractitioners refer patients to endodontists for thewhole procedure.

Endodontists and general practitioners obtainaccess through the crown significantly more oftenthan do prostbodontists (P < 0.001) and showed atrend toward maintaining tbe existing crown as thefinal restoration. Prosthodontists used the crown as aprovisional restoration or constructed a provisionalacrylic resin complete-coverage restoration. Tbisentry was statistically significant with regard to theresponse by both endodontists and general practition-ers (P< 0.001)-

Tbe overall response to the fourth question was 97%(528/543). Table 4 indicates the respondents' beliefsabout tbe importance of coronal leakage wben theendodontically treated, crowned tooth is restored. Allpractitioner groups had similarly high response rates;

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TABLE 1 Total survey return

Practitioners

EndodontistsProsthodontistsGênerai dentistsTotai

Sent

300300300900

Received

175166543

Response rate

67%58%55%60%

TABLE 2 Total response to survey's secondquestion (pulpal status)

Practitioners

EndodontistsProsthodontistsGeneral dentistsTotal

Response

191/20272/175120/166383/543

Rate

95%4 1 %72%7 1 %

TABLE 3 Method of obtaining access to puip chamber

Endodontists Prosthodontists

Method No. % No.

Access through crown 177/202 88 20/65Remove tne crown 14/202 7 22/65Use artificial provisronal crown 11/202 5 23/65Totai- 202/202 100 65/175

'Total number and percentage ot responses (o llie qiiesiion in reialion to Hie numbe

%

31343537

of surveys relu

Gênerai practitioners

No.

79/11529/115

7/115115/166

ned

%

6925

669

Ail practitioners

No.

276/38265/38241/382

382/543

%

72171170

TABLE 4

Response

A i waysFrequentiySeldomNeverTo1ai-

• Tata i number

Importance of coronal leakage when an access opening is restored through a crown

Endodontists

No.

177/19612/1967/1960/196

196/202

3nd percentage of responses to the que

%

90e40

97

lion in reiafio

Prosthodontists

No.

139/17114/17114/1714/171

171/175

n fo Ihe number

%

818e3

98

of sur

Gênerai practitioners

No.

124/16123/16112/1612/161

161/166

ueys returned.

%

771481

97

Ali practitioners

No.

440/52849/53833/528

6/528528/543

%

83971

97

TABLE 5 Age of the crown when a tooth requires nonsurgicai root canai treatment

Age ot orown

0-5 y5-10 y10 y or moreTotai'

EndodontÍ5ts

No.

74/153 4870/153 46

9/153 6153/202 76

Prosthodontists

No.

43/15183/15125/151

151/175

'Tolai number and peroenlage Of responses lo tiie question in reiation to the numbe

%

28551786

of surveys

Gênerai pracdtioners

No.

44/14880/14824/148

148/166

returned.

%

30541689

Aii practitioners

No.

161/452233/452

58/452452/543

%

36521383

at least 97% of each practitioner group responded to

the question. A chi-squared test of independence

revealed no statistically significant differences among

the 3 types of practitioners (endodontists, prosthodon-

tists, and general practitioners) in the perceived impor-

tance of restoring access openings.

The overall response to the question regarding the

age of the crown was 83% (452/543). While there was

no statistically significant difference in response rates

among the groups, endodontists had a lower response

rate (76%) than they had for the other questions. The

data in Table 5 indicate that a significantly greater

number of practitioners believe that crowned teeth

will require NSRCT in 5 to 10 years (P < 0.001).

When all responses were combined, 36% of practition-

ers (161/452) believed that teeth with complete-cover-

age crowns would require NSRCT in the first 5 years,

52% (233/452) expected it to be needed in the 5- to

10-year span, and 13% (58/452) predicted that it

would be necessary after 10 years or more.

716 Voiume 31 , Number 10, 2000

• Trautmann étal

DISCUSSION

The total response to the survey (60%) compares withthat attained by previous itivestigators who evaluated theresponse rates atnong dentists,='"-^= The low responserate of general practitioners (löo/o) necessitated the mail-ing of a second survey to obtain a sufficient representa-tive sample from the genera! practitioner population(55%), The final response was equivalent to the level ofresponse considered acceptable; a response rate of lessthan 50% in a dental population may be suspect,^*Hovland et al" found no differences in attitudes, knowl-edge, or demographic data in tiie group that needed anadditional request to return the questionnaire.

Endodontists (880.0) and general practitioners (69%)indicated that they create endodontic access openingsthrough complete-coverage crowns more often than doprosthodontists (31''.'o), Notably, a significant numberof prosthodontists (81%) indicated in the second ques-tion that they refer the endodontic treatment to theirspecialist of choice. Prosthodontists who initiateNSRCT (37%) remove the crown and subsequently useit as a provisional crown (34%), create an acrylic resinprovisional restoration {35tt'o), or create endodonticaccess openings through complete-coverage crowns.

The combination of extensive coronal restorations,such as crowns, and periodontal disease may have agreater impact on the viability of the dental pulp.Combined, all groups identified 5 to 10 years as themost common time period for pulpal demise in teethwith complete coverage restorations. Many endodon-tists (48%), however, identified pulpal degeneration ata much earlier stage, 1 to 5 years. This is attributableto the fact that endodontists treat pulpal inflammationand/or necrosis daily. Previous studies have identifiedthe life span of crowns to be in a range similar to the5- to 10-year range chosen in the survey,'̂ •'-̂ ^

The responses of the dental pulp to irritation,including caries, trauma, chemical insult, and thermalinsitJt are multiple. Microscopic infiammatory changesin the pulp may be present in the complete absence ofclinical symptoms and signs-^' Repeated episodes ofcaries, periodontal disease, and dental treatment arecumulative and ultimately approach a clinically signifi-cant threshold in which root canal treatment is essen-tial, even when the tooth is asymptomatic. These teethare not identified routinely and are said to exhibit astressed puip.^^ The data collected in this survey sug-gest that the concept of a stressed pulp is valid and istherefore an issue to be considered during the treat-ment planning phase of the restorative treatment-These data also indicate that specialists do limit theirpractice to their chosen field.

Several investigators have identified coronal leak-age as a major factor in bacterial contaminafion and

the subsequent failure of nonsurgical root canal fher-apy.5.20,21,23,24.39,40 Contamiiiafion of dentin by saliva andthe penetration of the dentinal tubules by bacteria andtheir by-products through leakage have a detrimentaleffect on pulpal fissue,^'-" Leakage around the marginof a cast restoration frequently extends toward thepulp through the dentinal tubules. This is a problemthat is extremely difficult to assess clinically and radi-ographicaiiy. The importance of the integrity of therestoration in the access opening and the crown there-fore cannot be understated,^ The importance of leak-age that can penetrate these coronal restorations isevidenced by the significant number of responses tothis question (97%); most respondents (83%) identi-fied leakage as always being significant.

CONCLUSION

The data presented constitutes the first part of a 4-partseries. The first 2 parts discuss the findings of a stirveysent to 900 active practifioners, resulting in the follow-ing conclusions;

1, Respondents to the survey believe that leakagemust be minimized when endodontic access open-ings are restored in artificial crowns on teeth thathave undergone nonsurgical root canal treatment,

2, Endodontists and general practitioners obtain accessthrough complete-coverage crowns and maintainthese crowns as final restorations more often thando prosthodontists. Prosthodontists obtain accessthrough the crowns, but replace the artificial crownsonce the treatment has been completed,

3, The trend among practifioners is to limit practice totheir specialty; however, general practitioners per-form nonsurgical root canal treatment more fre-quently than do prosthodontists,

4, A wide range of dental practitioners believe thatthe majority of teeth with complete-coverage fixedcrowns will require NSRCT in 5 to 10 years.

ACKNOWLEDGMENTS

This researcti was supported in part by ttie Intramural Grant of (heBaylor College of Dentistry, a member of the Tesas A&M Universicj'System Health Si;ieiice Center,

REFERENCES

1. Cheung GSP, A preliminary investigation into the longevityand causes of failure of single unit extracoronal restorations.I Dent 1991:19:160-163,

Quintessence International717

• Trautmann et ai

2, Bergenholtz G, Nyman S. Endodontie complications follow-ing periodontal and prosthetic treatment of patients withadvanced periodental disease, J Periodontol 1984;55:63-68.

3, Jackson CR, Skidmore AE, Rice RT. Pulpal evaluation ofteeth restored with fixed prostheses. J Prosthet Dent 1992;67:323-325.

4, Valderhaug J, Jokstad A, Ambjornsen E, Norheim PW.Assessment of the periapical and clinical status of crowni^dteeth over 25 years. J Dent 1997;25:97-105.

5, Näpänkagas R, Salonen MA, Raustia AM, A 10-year follow-up study of fixed metal ceramic prosthodontics. ] OralRehabil 1997;24;713-717

6, Goldman M, Laosonthom P, White RR, Microleakage-Ful Icrowns and dental pulp. ] Endod 1992;18.473-475.

7 Lowman IV, Burke RS, Pelleu GB. Patent accessory canals'Incidence in molar furcation region. Oral Surg Oral MedOral Pathol 1973;36:580-584.

8. Rubach WC, Mitchell DF. Periodontal disease, accessorycanals and pulp pathosis. J Periodontol 1955;36:34-38.

9, Langelarid K, Rodriguez H, Dowden W. Periodontal dis-ease, bacteria and pulpal histopathology. Oral Surg OralMed Oral Pathgl 1974;37:257-270,

10. Belk CE, Gutmann (L. Perspectives, controversies anddirectives on pulpal-periodontal relationships. J Can Di'ntAssoc 1990:56.1013-1017

11. Massler M, Pulpal reaction to dental caries. Tnt Dent ]1967; 17.441-460.

12. Torneck CD. A report of studies into changes in the finestructure of the dental pulp human caries pulpitis. \ Endod1981;7:8-16.

13. Langeland K, Tissue response to dental caries. Endüd DentTraumatoi 1987:3:149-171,

14. Bergenholtz G|. Pathugenic mcL-hanisms in pulpal disease.J Endod 1990;16 98-10! .

15. Langeland K. Histoiogic evaluation of pulp reactions tooperative procedures. Oral Surg Oral Med Oral Pathol1959;12:1235-124H,

16. Langeland K. Histolugic evaluation of pulp reactions tooperative procedures Oral Surg Oral Med Oral Pathol1959:12:1357-1369.

17 Langeland K, Effects of various procedures on the humandental pulp. Oral Surg Oral Med Oral Pathol 1961;14:210-233.

18. Langeland K, Langeland LK. Pulp reactions to crownpreparations, impression, temporary crown fixation, andpermanent cementation. ] Prosthet Dent 1965;15:129-143,

19. Bergenholtz G], Cox CG. Loesche W|, Syed SA. Bacterialleakage around dental restorations: its effect in the dentalpulp. J Oral Pathol 1982;Il:439-450.

20. Cox CF, Keall CL, Keall HJ, Ostro E, Bergenholtz, G|.Biocompatibility of surface-scaled dental materials againstexposed pulps, ] Prosthet Dent 1987;57:l-8,

21 . Madison S, Wilcox LR. An evaluation of coronal microleak-age in endodontically treated teeth. Part Ul. In vivo study.J Endod 1988; 14:455-45 8,

22. Seltzer S, Bender IB. The Dentai Pulp: Biologic Consid-erations in Dental Procedures, ed 3, St Louis: IshiyakuEuroameriea, 1990:349-373.

23. Saunders WP, Saunders EM, Coronal leaicage as a cause offailure in root canal therapy: A review. Endod DentTraumatoi 1994;10:105-108.

24. Wu M-K, Wesseiink PR. Endodontic leakage studies recon-sidered. Part 1. Methodology, application and relevance. IntEndod) 1993;26:37-43.

25. Jeffrey IWM, Saunders WP. An investigation into the bondstrength between a root canal sealer and root filling points,Int Endod ] 1987;20:217-222,

26. Ray H, Trope M. Periapica! status of endodontically treatedteeth in relation to the quality of the root filling and thecoronal restoration. Int Endod J 1995;28:12-18.

27. Hovland E], Romberg E, Moreland EP Non response biasto mail survey questionnaires within a professional popula-tion. ] Dent Educ 1980:44:270-274.

28. Hovland E], Gutmann JL. How is mail survey questionnaireused in research? Dent Hyg 1980;54:410,

29 Stamos DE, Gutmann JL. Survey of endodontic retreatmentmethods used to remove intraradicular posts. J Endod 1993;19:366-369,

30. Trautmann G, Gutmann )L, Nunn ME, Witherspoon DE,Shuiman JD. Restoring teeth that are endodontically treatedthrough existing crowns. II. Survey of restorative materialscommonly used. Quintessence Int 2000;31:719-728.

31. Cafferta GL, Goldberg HJ, Roghmann K, Eox R. Continuingeducation: Attitudes, interests, and experiences of practicingdentists J Dent Educ 1975;39:793-800.

32. Hovland EJ, Gutmann JL, Current endodontic therapy pro-vided by the Maryland general dentist. J Md State DentAssoc 1978 ;21:14-20,

33. Wasilkoff PC, Maurice CG. Role of endodontics in currentdental practice. J Am Dent Assoc 1976;93:800-805.

34 Schwartz NL, Whitsett LD, Berry TG, Stewart JL. Unserv-iceable crowns and nxed partial dentures. Lifespan and causesfor loss of seraceability. J Am Dent Assoc 1970;81:1395-1401.

35. Wahon JN, Gardner FM, Agar JR, A survey of erown andfixed partial denture failures: Length of service and reasonsfor replacement, J Prosthet Dent 1986;56:416-421.

36 Glantz PO, Ryge G, Jendresen MD, Nilner K, Quality cfextensive fixed prostiiodontics after five years. J ProsthetDent 1984:52475-479.

37 Reeves R, Stanley HR. The relationship of bacterial penetra-tion and pulpal pathosis in carious teeth. Oral Surg OralMed Orai Pathol 1966;22;59-65.

38. Abou-Rass M. The stressed pulp condition: An endodontic-restorative diagnostic concept. J Prosthet Dent 1982;48;264-267.

39. Saunders WP. Saunders EM. Assessment of leakage in therestored pulp chamber of endodontically treated multi-rooted teeth. Int Endod J 1990;23:28-33.

40. Magura ME, Kafrawy AH, Brown CE Jr, Newton CW.Human saliva coronal microleakage in obturated rootcanals: An in vitro study. J Endod 1991;17:324-331.

41. Kakehashi S, Stanley HR, Fitzgerald RJ. The effects of surgi-cal exposures of dental pulps in germ-free and conventionallaboratory rats. Oral Surg Oral iVied Oral Pathol 1965;20:340-349,

42. Bergenholtz GJ, Lindhe J. Effect of soluble plaque factorson inflammatory reactions in the dental pulp. Scand J DentRes 1975;83:153-158.

43. Bergenhoitz GJ Effects of bacterial products on inflamma-tory reactions in the dental puip bacteria. Scand J Dent Res1977;85;122-129,

44. Bergenhoitz GJ, Inflammatory response of the dental pulpto bacterial irritation, J Endod 1981 ;7:100-104.

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